1. Field of Invention
The invention relates to operating voltage levels of integrated circuits. In particular, the invention relates to apparatus and methods for translating voltage levels of signals traveling between integrated circuits that operate at different voltage levels.
2. Discussion of Related Art
Electronic systems often include circuits that operate at relatively low voltages, at times including core logic circuits and memory circuits, and other circuits that operate at higher voltages. Such mixed-mode voltage systems typically require voltage translation and voltage clamping capabilities. Voltage translation components allow proper communication of the I/O signals traveling between circuits operating at different voltage levels.
Circuits that employ transistors having smaller gate dimensions typically require an associated decrease in supply voltage level. Microprocessors and memory circuits, for example, often are fabricated with transistors having the smallest possible gate sizes. Thus, electronic systems, such as a cellular telephones and personal computers, will typically have components, such as processors, that operate at a low internal voltage, and additional components that operate at a relatively high external voltage. While an internal voltage supply may provide, for example, 2.5V, 1.5V or 0.9V, external voltage supplies may provide, for example, 5V, 3.3V or 2.5V.
Voltage translation circuits can provide uni- or bidirectional conversion of the low- and high-voltage signals produced by the circuits using the different supply voltage levels. Often, for example, a level-shifting circuit is used to increase the upper voltage-level swing of the low-voltage signals produced by high-performance complimentary metal-oxide-semiconductor (CMOS) logic devices. Unfortunately, a level-shifting circuit may fail to function properly when an internal voltage supply is producing less than its full operating voltage. Moreover, level-shifting circuits can introduce distortions and/or delays in the low-voltage signals that they convert to high-voltage signals.